<!--
 * @Author: your name
 * @Date: 2022-02-05 09:25:57
 * @LastEditTime: 2022-02-05 18:06:01
 * @LastEditors: DESKTOP-EH1PJNP
 * @Description: 呼吸嵌套圆
 * @FilePath: \xxtx_ui-demod:\Qweb\html\html\day04\3-circle.html
-->
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>嵌套圆</title>
  <style>
    .outer , .inner {
      box-sizing: border-box; /* width : padding + border + 内容*/
      border-radius: 50%;
    }
    .outer {
      width: 300px;
      height: 300px;
      border: 3px solid #ccc;
      margin: 0 auto;
      padding: 50px;
      transition: padding 2s;    /*类呼吸灯效果*/
    }
    .outer:hover {
      padding: 10px;
    }
    .outer .inner {
      width: 100%;
      height: 100%;
      border: 5px solid #ccc;
    }
  </style>
</head>
<body>
  <div class="outer">
    <div class="inner">

    </div>
  </div>
</body>
</html>